How to get MAC address of your machine using a C program?

Question

I am working on Ubuntu. How can I get MAC address of my machine or an interface say eth0 using C program.

Please see also related question: https://stackoverflow.com/questions/4951257/using-c-code-to-get-same-info-as-ifconfig — Keeely, Nov 23 '18 at 09:55

score 153 · Answer 1 · edited Jul 10 '17 at 08:54

153

Much nicer than all this socket or shell madness is simply using sysfs for this:

the file /sys/class/net/eth0/address carries your mac adress as simple string you can read with fopen()/fscanf()/fclose(). Nothing easier than that.

And if you want to support other network interfaces than eth0 (and you probably want), then simply use opendir()/readdir()/closedir() on /sys/class/net/.

edited Jul 10 '17 at 08:54

haccks

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answered Nov 22 '09 at 23:11

user175104

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Good answer, but not applicable in all situations. e.g. embedded systems (especially older ones, such as old versions of busybox, that don't have sysfs nor can support it because the system itself may be too old) – Alex Marshall Apr 15 '13 at 12:45
3

The question specifically asked for a C solution – Charles Salvia Jun 19 '14 at 01:48
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@CharlesSalvia opening and reading a system file still seems like a C solution... as long as you know what your target system provides! Granted, your program will be tied to that type of system. But just compiling a program ties it to a system's architecture. I think this answer will help in many (but not all) situations. – moodboom Dec 29 '16 at 14:53
(using Debian derived Bunsen on WiFi) See: /sys/class/net/wlp2s0/address – AAAfarmclub Sep 12 '20 at 23:30
Introducing fscanf for something that can be done with a portable C-API (e.g getifaddrs), instead is true madness. This solution is neither portable, nor safe, nor future proof. https://docs.kernel.org/admin-guide/sysfs-rules.html – The19thFighter Jul 26 '23 at 11:15

score 72 · Accepted Answer · edited May 25 '12 at 00:35

72

You need to iterate over all the available interfaces on your machine, and use ioctl with SIOCGIFHWADDR flag to get the mac address. The mac address will be obtained as a 6-octet binary array. You also want to skip the loopback interface.

#include <sys/ioctl.h>
#include <net/if.h> 
#include <unistd.h>
#include <netinet/in.h>
#include <string.h>

int main()
{
    struct ifreq ifr;
    struct ifconf ifc;
    char buf[1024];
    int success = 0;

    int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
    if (sock == -1) { /* handle error*/ };

    ifc.ifc_len = sizeof(buf);
    ifc.ifc_buf = buf;
    if (ioctl(sock, SIOCGIFCONF, &ifc) == -1) { /* handle error */ }

    struct ifreq* it = ifc.ifc_req;
    const struct ifreq* const end = it + (ifc.ifc_len / sizeof(struct ifreq));

    for (; it != end; ++it) {
        strcpy(ifr.ifr_name, it->ifr_name);
        if (ioctl(sock, SIOCGIFFLAGS, &ifr) == 0) {
            if (! (ifr.ifr_flags & IFF_LOOPBACK)) { // don't count loopback
                if (ioctl(sock, SIOCGIFHWADDR, &ifr) == 0) {
                    success = 1;
                    break;
                }
            }
        }
        else { /* handle error */ }
    }

    unsigned char mac_address[6];

    if (success) memcpy(mac_address, ifr.ifr_hwaddr.sa_data, 6);
}

edited May 25 '12 at 00:35

Jamesprite

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answered Nov 22 '09 at 19:48

Charles Salvia

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Why does this not need struct in front if ifreq and ifconf? Were typedefs for these structs removed in more recent kernels, that existed in 2009 when this was written? – Karl P Jul 20 '11 at 17:39
I think it should be noted that OpenVZ containers do not have a MAC address and therefore, none of these solutions would work. The MAC address is (assumed to be) ``00:00:00:00:00:00`` – SameOldNick Feb 22 '14 at 07:19
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It only works if there is link on eth0. It doesn't work if the network cable is unplugged (on Ubuntu). – Florin Petriuc Jul 24 '14 at 15:07
8

Perhaps close(sock)? – Art Swri Feb 09 '16 at 21:17
@ArtSwri I think you were right,maybe error hanle goto some LABLE and close(sock) – J.Doe Apr 15 '19 at 16:27
Hi I have been looking at this code. I understand most of it except for the `break`. According to your logic if it is not loopback then it must be the active ethernet or wifi. what if there is more than one active interface with address then due to break u will only get the 1st active interface with address. Or is it like a computer can only have one active network interface with address at a time? Can anyone please explain the `break` part? – DirtyV Apr 08 '23 at 05:38
Like my question is if that is the case why even have a loop. Can we not just add 1 to `it` pointer and say that its the only active network interface with address? – DirtyV Apr 08 '23 at 05:57

score 28 · Answer 3 · answered Nov 22 '09 at 19:47

28

You want to take a look at the getifaddrs(3) manual page. There is an example in C in the manpage itself that you can use. You want to get the address with the type AF_LINK.

answered Nov 22 '09 at 19:47

Juliano

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in the manpage of getifaddrs linked the type `AF_LINK` is not described. Perhaps this is superseded by `AF_PACKET` ? – mpromonet Feb 06 '16 at 15:15
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According to https://stackoverflow.com/a/26038501/5230867 it seems that AF_LINK is macOS/BSD-specific, while AF_PACKET is the Linux equivalent. – Manfred Urban Sep 26 '18 at 23:05

score 26 · Answer 4 · edited Oct 18 '11 at 08:10

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#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/if.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>

int main()
{
  struct ifreq s;
  int fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);

  strcpy(s.ifr_name, "eth0");
  if (0 == ioctl(fd, SIOCGIFHWADDR, &s)) {
    int i;
    for (i = 0; i < 6; ++i)
      printf(" %02x", (unsigned char) s.ifr_addr.sa_data[i]);
    puts("\n");
    return 0;
  }
  return 1;
}

edited Oct 18 '11 at 08:10

Jamesprite

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answered Nov 22 '09 at 20:02

Employed Russian

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Don't forget to error check socket() and close the socket if it opened successfully. – Anonymouse Jan 17 '20 at 09:23

mpromonet · Answer 5 · 2019-06-07T05:56:23.070

Using getifaddrs you can get MAC address from the family AF_PACKET.

In order to display the MAC address to each interface, you can proceed like this:

#include <stdio.h>
#include <ifaddrs.h>
#include <netpacket/packet.h>

int main (int argc, const char * argv[])
{
    struct ifaddrs *ifaddr=NULL;
    struct ifaddrs *ifa = NULL;
    int i = 0;

    if (getifaddrs(&ifaddr) == -1)
    {
         perror("getifaddrs");
    }
    else
    {
         for ( ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next)
         {
             if ( (ifa->ifa_addr) && (ifa->ifa_addr->sa_family == AF_PACKET) )
             {
                  struct sockaddr_ll *s = (struct sockaddr_ll*)ifa->ifa_addr;
                  printf("%-8s ", ifa->ifa_name);
                  for (i=0; i <s->sll_halen; i++)
                  {
                      printf("%02x%c", (s->sll_addr[i]), (i+1!=s->sll_halen)?':':'\n');
                  }
             }
         }
         freeifaddrs(ifaddr);
    }
    return 0;
}

Ideone

score 12 · Answer 6 · answered Jun 24 '14 at 12:45

I have just write one and test it on gentoo in virtualbox.

// get_mac.c
#include <stdio.h>    //printf
#include <string.h>   //strncpy
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>   //ifreq
#include <unistd.h>   //close

int main()
{
    int fd;
    struct ifreq ifr;
    char *iface = "enp0s3";
    unsigned char *mac = NULL;

    memset(&ifr, 0, sizeof(ifr));

    fd = socket(AF_INET, SOCK_DGRAM, 0);

    ifr.ifr_addr.sa_family = AF_INET;
    strncpy(ifr.ifr_name , iface , IFNAMSIZ-1);

    if (0 == ioctl(fd, SIOCGIFHWADDR, &ifr)) {
        mac = (unsigned char *)ifr.ifr_hwaddr.sa_data;

        //display mac address
        printf("Mac : %.2X:%.2X:%.2X:%.2X:%.2X:%.2X\n" , mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
    }

    close(fd);

    return 0;
}

score 6 · Answer 7 · edited Jul 14 '20 at 07:47

Assuming that c++ code (c++11) is okay as well and the interface is known.

#include <cstdint>
#include <fstream>
#include <streambuf>
#include <regex>

using namespace std;

uint64_t getIFMAC(const string &ifname) {
  ifstream iface("/sys/class/net/" + ifname + "/address");
  string str((istreambuf_iterator<char>(iface)), istreambuf_iterator<char>());
  if (str.length() > 0) {
    string hex = regex_replace(str, std::regex(":"), "");
    return stoull(hex, 0, 16);
  } else {
    return 0;
  }
} 
int main()
{
  string iface = "eth0";
  printf("%s: mac=%016llX\n", iface.c_str(), getIFMAC(iface));
}

score 0 · Answer 8 · answered Nov 22 '09 at 19:44

0

On Linux, use the service of "Network Manager" over the DBus.
There is also good'ol shell program which can be invoke and the result grabbed (use an exec function under C):

$ /sbin/ifconfig | grep HWaddr

answered Nov 22 '09 at 19:44

jldupont

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score 0 · Answer 9 · edited Jan 25 '16 at 14:03

0

A very portable way is to parse the output of this command.

ifconfig | awk '$0 ~ /HWaddr/ { print $5 }'

Provided ifconfig can be run as the current user (usually can) and awk is installed (it often is). This will give you the mac address of the machine.

edited Jan 25 '16 at 14:03

mpromonet

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answered Nov 22 '09 at 19:54

hookenz

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It's not very portable at all. It gives nothing on Mac OS X. The output of `ifconfig` does not contain the text `HWaddr`. – dreamlax Nov 22 '09 at 20:25
Had to do this earlier in the year on solaris, linux and hpux. – hookenz Nov 22 '09 at 22:04
1

Well, the concept is portable. The text may need tweaking for other platforms. – hookenz Nov 22 '09 at 22:05
2

Using shell scripts, even one as tiny as yours is far from portable. There is a joke that goes that a shell is easier to port than a shell script :p – sigjuice Nov 23 '09 at 01:59
8

Also, this isn't going to compile in any C compiler I know of. – BobbyShaftoe Nov 23 '09 at 14:10
there is no `ifconfig` on debian stretch. not portable at all. – totten Feb 05 '18 at 09:05

score 0 · Answer 10 · answered Oct 17 '17 at 22:55

Expanding on the answer given by @user175104 ...

std::vector<std::string> GetAllFiles(const std::string& folder, bool recursive = false)
{
  // uses opendir, readdir, and struct dirent.
  // left as an exercise to the reader, as it isn't the point of this OP and answer.
}

bool ReadFileContents(const std::string& folder, const std::string& fname, std::string& contents)
{
  // uses ifstream to read entire contents
  // left as an exercise to the reader, as it isn't the point of this OP and answer.
}

std::vector<std::string> GetAllMacAddresses()
{
  std::vector<std::string> macs;
  std::string address;

  // from: https://stackoverflow.com/questions/9034575/c-c-linux-mac-address-of-all-interfaces
  //  ... just read /sys/class/net/eth0/address

  // NOTE: there may be more than one: /sys/class/net/*/address
  //  (1) so walk /sys/class/net/* to find the names to read the address of.

  std::vector<std::string> nets = GetAllFiles("/sys/class/net/", false);
  for (auto it = nets.begin(); it != nets.end(); ++it)
  {
    // we don't care about the local loopback interface
    if (0 == strcmp((*it).substr(-3).c_str(), "/lo"))
      continue;
    address.clear();
    if (ReadFileContents(*it, "address", address))
    {
      if (!address.empty())
      {
        macs.push_back(address);
      }
    }
  }
  return macs;
}

score 0 · Answer 11 · answered Sep 11 '20 at 05:36

netlink socket is possible

man netlink(7) netlink(3) rtnetlink(7) rtnetlink(3)

#include <assert.h>
#include <stdio.h>
#include <linux/if.h>
#include <linux/rtnetlink.h>
#include <unistd.h>

#define SZ 8192

int main(){

  // Send
  typedef struct {
    struct nlmsghdr nh;
    struct ifinfomsg ifi;
  } Req_getlink;
  assert(NLMSG_LENGTH(sizeof(struct ifinfomsg))==sizeof(Req_getlink));
  int fd=-1;
  fd=socket(AF_NETLINK,SOCK_RAW,NETLINK_ROUTE);
  assert(0==bind(fd,(struct sockaddr*)(&(struct sockaddr_nl){
    .nl_family=AF_NETLINK,
    .nl_pad=0,
    .nl_pid=getpid(),
    .nl_groups=0
  }),sizeof(struct sockaddr_nl)));
  assert(sizeof(Req_getlink)==send(fd,&(Req_getlink){
    .nh={
      .nlmsg_len=NLMSG_LENGTH(sizeof(struct ifinfomsg)),
      .nlmsg_type=RTM_GETLINK,
      .nlmsg_flags=NLM_F_REQUEST|NLM_F_ROOT,
      .nlmsg_seq=0,
      .nlmsg_pid=0
    },
    .ifi={
      .ifi_family=AF_UNSPEC,
      // .ifi_family=AF_INET,
      .ifi_type=0,
      .ifi_index=0,
      .ifi_flags=0,
      .ifi_change=0,
    }
  },sizeof(Req_getlink),0));

  // Receive
  char recvbuf[SZ]={};
  int len=0;
  for(char *p=recvbuf;;){
    const int seglen=recv(fd,p,sizeof(recvbuf)-len,0);
    assert(seglen>=1);
    len += seglen;
    if(((struct nlmsghdr*)p)->nlmsg_type==NLMSG_DONE||((struct nlmsghdr*)p)->nlmsg_type==NLMSG_ERROR)
      break;
    p += seglen;
  }

  struct nlmsghdr *nh=(struct nlmsghdr*)recvbuf;
  for(;NLMSG_OK(nh,len);nh=NLMSG_NEXT(nh,len)){
    if(nh->nlmsg_type==NLMSG_DONE)
      break;

    struct ifinfomsg *ifm=(struct ifinfomsg*)NLMSG_DATA(nh);

    printf("#%d ",ifm->ifi_index);
    #ifdef _NET_IF_H
    #pragma GCC error "include <linux/if.h> instead of <net/if.h>"
    #endif

    // Part 3 rtattr
    struct rtattr *rta=IFLA_RTA(ifm); // /usr/include/linux/if_link.h
    int rtl=RTM_PAYLOAD(nh);

    for(;RTA_OK(rta,rtl);rta=RTA_NEXT(rta,rtl))switch(rta->rta_type){
    case IFLA_IFNAME:printf("%s ",(const char*)RTA_DATA(rta));break;
    case IFLA_ADDRESS:
      printf("hwaddr ");
      for(int i=0;i<5;++i)
        printf("%02X:",*((unsigned char*)RTA_DATA(rta)+i));
      printf("%02X ",*((unsigned char*)RTA_DATA(rta)+5));
      break;
    case IFLA_BROADCAST:
      printf("bcast ");
      for(int i=0;i<5;++i)
        printf("%02X:",*((unsigned char*)RTA_DATA(rta)+i));
      printf("%02X ",*((unsigned char*)RTA_DATA(rta)+5));
      break;
    case IFLA_PERM_ADDRESS:
      printf("perm ");
      for(int i=0;i<5;++i)
        printf("%02X:",*((unsigned char*)RTA_DATA(rta)+i));
      printf("%02X ",*((unsigned char*)RTA_DATA(rta)+5));
      break;
    }

    printf("\n");

  }

  close(fd);
  fd=-1;
  return 0;

}

Example

#1 lo hwaddr 00:00:00:00:00:00 bcast 00:00:00:00:00:00
#2 eth0 hwaddr 57:da:52:45:5b:1a bcast ff:ff:ff:ff:ff:ff perm 57:da:52:45:5b:1a
#3 wlan0 hwaddr 3c:7f:46:47:58:c2 bcast ff:ff:ff:ff:ff:ff perm 3c:7f:46:47:58:c2

score -1 · Answer 12 · answered Jul 25 '18 at 12:29

-1

This is a Bash line that prints all available mac addresses, except the loopback:

for x in `ls /sys/class/net |grep -v lo`; do cat /sys/class/net/$x/address; done

Can be executed from a C program.

answered Jul 25 '18 at 12:29

LachoTomov

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How to get MAC address of your machine using a C program?

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